Handheld electronic devices such as smartphones, tablets, and smartwatches are popular with consumers and are sold in great numbers. The majority of these devices employ a touch sensitive display for both display of output to a user and accepting data as input from a user. Most of these touch sensitive displays utilize capacitive touch sensing.
A typical such touch sensitive display includes a display layer constructed from technology such as LCD, IPS, or AMOLED, as well as a sensing layer. A typical sensing layer includes a plurality of parallel drive lines, and a plurality of parallel sense lines. The sense lines capacitively intersect the drive lines. In operation, a single drive line is driven with a wave, such as a square wave or sine wave having a period of typically 2.5 μs. The capacitance between the sense lines and the driven drive line is sensed at the point where they intersect. Presence of a human finger or a conductive object alters the expected capacitance at the intersection point, and by measuring the change in capacitance, a touch between the finger or object and the touch sensitive display can be detected.
Consumer desires for these handheld electronic devices are for the devices to grow increasingly thin. This accordingly results in the desire to make touch sensitive displays increasingly thin. However, as such touch sensitive displays grow thinner, noise from the display layer becomes an increasing problem for the sensing layer, as the thinner designs result in greater parasitic capacitances coupling the noise from the display layer through to the sensing layer. This noise, when coupled through to the sensing layer, degrades accuracy of the touch sensing performed by the sensing layer, which is commercially undesirable.
One way to help avoid noise in touch sensing is to perform the touch sensing (sampling) at times during which less noise is present. However, since this involves a constraint on the length of time per second available for sampling, it can degrade touch sensing performance due to the fewer number of samples collected.
Therefore, noise reduction techniques which provide for collection of an increased number of samples are desirable.